1. Technical Field
The present invention relates to a manufacturing method of metal oxide nanostructure and an electronic element comprising the same. More particularly, the present invention relates to a manufacturing method of metal oxide nanostructure, in which, in the growth of metal oxide nanostructure, a ternary amorphous layer and a single crystal layer are formed on a native binary amorphous layer by spontaneous phase separation, and thus the diameter and density of metal oxide nanostructure are controlled depending on the relative size of the ternary amorphous layer.
2. Description of the Related Art
Generally, field emission devices include nanostructure having sharp tips, and serve to emit electrons from their tips using the electric field applied to the nanostructure. Field emission devices are practically being used in various electronic apparatuses, for example, field emission displays, X-ray sources, beam lasers, microwave power amplifiers, and various sensors such as biosensors. In these applied products, field emission devices must be embodied such that electrons easily tunnel even at low voltage. That is, it is required that field emission devices be provided with nanostructure which can minimize the diameter of a tip and the work function of the surface of the tip.
In order to realize such nanostructure, research into the structure and material of nanostructure has been made in various ways. As a result, carbon nanotubes (nanowires) or metal oxide semiconductors have attracted considerable attention as materials used in the nanostructure. These materials have been noticed because they have excellent mechanical, thermal and electrical stability.
However, carbon nanotubes are difficult to vertically orient although various growth methods have been proposed. Further, carbon nanotubes have low aspect ratios and poor thermal and mechanical stability compared to metal oxide semiconductors.
Meanwhile, vertical type nanostructure prepared using metal oxide semiconductors can be epitaxially grown using a metal catalyst. Concretely, in the epitaxial growth method, the vertical type nanostructure are grown by patterning a silicon substrate with a metal catalyst such as gold (Au) or the like, which are widely used to fabricate metal oxide nanowires, using photography and then supplying a zinc-containing precursor onto the silicon substrate.
Such epitaxial growth using chemical vapor deposition (CVD) may be performed by a vapor-liquid-solid mechanism (VLS). According to this method, as nanostructure grow, gold (Au) constituting the seed moves to the tips of the nanostructure, and zinc (Zn) moves to the lower ends thereof.
The metal catalyst causes problems such as deterioration in the optical characteristics due to nonluminescent recombination, difficulty in controlling the conductivity of nanowires, deterioration in orientation of nanowires, and the like. In order to solve these problems, various methods have been attempted.
For example, nanowires can be formed by an epitaxial growth method using metalorganic chemical vapor deposition (MOCVD) in which a vapor-solid (VS) mechanism is applied. In this method, the growth of nanowires can be performed without using a metal catalyst. However, during the metalorganic chemical vapor deposition (MOCVD) process, the growth direction of nanowires and the formation of native interface layers are influenced by temperature.
FIGS. 1 to 3 are sectional views showing a conventional process of forming metal oxide nanostructure at low temperature. In FIGS. 1 to 3, the conventional process is performed at a temperature of 400˜450° C.
Referring to FIG. 1, a zinc-containing precursor 14 is supplied onto a silicon substrate 10 so that nuclei 12 are formed on the silicon substrate 10 with the nuclei 12 spaced apart from each other. In this case, the nuclei 12 have a size much smaller than that of metal seeds used in chemical vapor deposition (CVD). That is, the size of the nuclei 12 is on the atomic unit scale.
Referring to FIG. 2, in the procedure of supplying the zinc-containing precursor 14 onto the silicon substrate 10 including the nuclei 12, the nuclei 12 formed on the silicon substrate spread and agglomerate with other adjacent nuclei 12 to form grown nuclei 12a having a size smaller than that of metal seeds.
Referring to FIG. 3, when a source gas 15 including a zinc-containing precursor and oxygen gas is supplied thereto with the process temperature maintained at 400˜450° C., the grown nuclei 12a are vertically grown by the supply of source gas 15, thus forming high-density nanostructure 18.
According to this method, the nanostructure 18 can be grown in a direction perpendicular to the silicon substrate 10, but native interface layers 16 can be formed between the silicon substrate 10 and the nanostructure 18 in the process of forming the nanostructure 18. Here, each of the native interface layers is disposed at the lower end of each of the nanostructure 18, and such defects as electric potential are concentrated therein. Therefore, at the time that the device is operated, the native interface layers inhibit electrons from moving in the nanostructure 18.
FIGS. 4 to 6 are sectional views showing a conventional process of forming metal oxide nanostructure at high temperature. In FIGS. 4 to 6, the conventional process is performed at a temperature of about 500° C., which is higher than that in the above-mentioned conventional process.
Referring to FIG. 4, a zinc-containing precursor 14 is supplied onto a silicon substrate 10, and thus nuclei 20 are formed on the silicon substrate 10 with nuclei 20 spaced apart from each other. In this case, the nuclei 20 can agglomerate with a larger amount of adjacent nuclei 20 because they can rapidly spread out and move on the silicon substrate 10. Therefore, the size of the nuclei 20 formed at high temperature is larger than that of the nuclei 12 formed at low temperature.
Referring to FIG. 5, in the procedure of supplying the zinc-containing precursor 14 onto the silicon substrate 10 including the nuclei 20, the nuclei 20 more actively grow to form a seed layer 22 having a size similar to that of metal seeds.
Referring to FIG. 6, source gas 23 including a zinc-containing precursor and oxygen gas is supplied onto the seed layer 22, thus forming nanostructure 24. In this high-temperature process, native interface layers are not formed unlike by the above low-temperature process, whereas the seed layer 22 may have various crystal orientations depending on the growth orientation of the nuclei 20 constituting the seed layer 22. Therefore, since the seed layer 22 does not grow in a direction perpendicular to the silicon substrate 10, the seed layer 22 grows into radial nanostructure 24 having various growth orientations.
Meanwhile, it is typically required that the above field emission devices used in electronic apparatuses directionally emit electrons. For this reason, the fact that the nanostructure 24 do not vertically grow does not comply with this requirement. Further, since the nanostructure 24 are not vertically aligned, it is difficult to conduct subsequent processes.
Thus, the present inventors have researched metal oxide nanostructure which can be vertically aligned and improve field emission characteristics. Concretely, they have researched forming metal oxide nanostructure using a single-crystalline seed layer including a first metal as a main component and an amorphous layer including a second metal as a main component formed on a substrate.
In particular, amorphous layers may occupy larger areas than do seed layers depending on such process conditions as relative flow rates of reactants, pressure and temperature in a chamber and the like in the procedure of supplying reaction gas. Owing to this fact, it was found that it is possible to control the density and diameter of seed layers. Since metal oxide nanostructure are formed by vertically growing the seed layers, the density and diameter of the metal oxide nanostructure can be controlled by controlling the relative areas of the amorphous layers to the seed layers.